The present invention relates to an anti-balloon device or the like, typically but not exclusively for weft feeders for weaving looms, and particularly for pre-measuring weft feeders for air jet looms.
As is known to the expert in the field, weft feeders are devices which are inserted between the spool and the loom and have the specific task of feeding the thread to the loom at each weft insertion, releasing it from a weft reserve accumulated by the device in the form of turns wound on a drum of the device; they also have the task of restoring the reserve by winding again onto the drum a number of turns equal to the unwound ones. Pre-measuring feeders furthermore have the task of measuring the length of thread released at each insertion, and for this purpose a pre-measuring feeder typically comprises a variable-diameter drum, on which a swiveling arm winds the turns that form the weft reserve, a weft braking finger for stopping the thread, which is associated with the drum and is actuated electromagnetically in order to release the thread, allowing it to unwind from the drum, and stop its unwinding once the pre-measured amount is reached, means for counting the turns released at each insertion, and means for counting the turns wound again in order to restore the weft reserve.
In devices of this type, due to the speed with which the turns of the reserve unwind from the drum, which is particularly high in pre-measuring feeders when the weft braking finger moves to the release position, the thread, urged by centrifugal force, arranges itself immediately downstream of the drum along the generatrices of a solid of revolution which is commonly known as xe2x80x9cballoonxe2x80x9d, whose dimensions increase as the speed of the weaving process increases and as the mechanical tension of the thread decreases. It is well-known that the presence of the balloon causes severe problems in the weaving process, since it facilitates the formation of tangles of thread, knots and other discontinuities which interfere with the correct travel of the thread, often causing it to break.
In order to avoid these drawbacks, the above weft feeders are equipped with anti-balloon devices placed downstream of the drum on which the weft reserve is wound and having the task of restraining the thread as much as possible, thus reducing its tendency to expand radially due to centrifugal force.
Known anti-balloon devices are typically constituted by shield-like elements having a preferably frustum-shaped continuous lateral surface or skirt and forming a through cavity for the thread, the shield-like elements being arranged with their major base directed toward the drum; the shield-like elements receive the unwinding thread and guide it toward a terminal thread guiding ring, from which the thread is sent to the loom. Inside said frustum-shaped shield-like element, the thread rotates like the hand of a clock and remains, due to centrifugal force, in contact with the internal lateral surface of said shield-like element; this entails a double drawback. Firstly, the friction generated by contact between the thread and the lateral surface brakes the thread, subjecting it to an undesirable mechanical tension which increases as travel speed of the thread increases and as the friction between the thread and the lateral surface increases; secondly, rotation like the hand of a clock and the consequent sliding of the thread in contact with the lateral surface of the shield-like element generates lint and dust, which in turn jam the correct advancement of the thread, damaging the correct execution of the weaving process.
In an attempt to obviate these drawbacks and particularly to reduce the mechanical tension generated on the thread by its sliding against the internal lateral surface of the frustum-shaped shield-like element, it has been suggested to give a profile to said surface by providing it, for this purpose, with raised ridges protruding radially inside the lateral surface.
According to the prior EP-A3-449068, an anti-balloon device is provided in which the ridges protruding from the internal lateral surface of the frustum-shaped shield-like element trace a spiral shape around the longitudinal axis of the element. Additionally, according to the EP-0737161, the internal lateral surface of the shield-like element of the anti-balloon device is instead provided with straight protruding ridges which are orientated along the generatrices of said surface.
However, both these known solutions have failed to give the expected results.
With the spiral ridge arrangement, the thread in fact remains in any case in contact with the ridge and the braking action produced by friction does not vary significantly, owing to the fact that the decrease in contact surface between the ridge and the thread is mostly compensated, for an equal centrifugal force, by the increase in the specific pressure urging the thread against the ridge. Even with the straight-ridge arrangement, the total braking action applied by the anti-balloon device to the thread does not vary significantly, owing to the fact that in passing from one ridge to the next the thread slides at least over part of the lateral surface separating one ridge from the next, so that as a whole the friction between the lateral surface and the thread does not vary appreciably.
The aim of the present invention is to eliminate the above drawbacks.
Within this general aim, an important and particular object of the present invention is to provide an anti-balloon device for weft feeders as specified, which is suitable to effectively contain the unwinding thread and at the same time significantly reduce the friction applied to the thread and the mechanical tension accordingly generated thereon, particularly so as to make the friction adjustable according to the operating requirements.
Another important particular object of the present invention is to provide a self-cleaning anti-balloon device, i.e., an anti-balloon device which does not accumulate dust, lint and the like generated by the sliding of the thread and by its interaction with the anti-balloon device.
Another object of the invention is to provide an anti-balloon device which has a simplified structure, with replaceable components, reduced weight and bulk and suitable to allow effective and broad adjustment of the braking action applied to the thread, thus making the device suitable for threads of any count and type.
According to the present invention, this aim and these and other objects which will become better apparent from the detailed description that follows are achieved with an anti-balloon device, typically but not exclusively for textile thread feeders, particularly pre-measuring weft feeders as specified, having the specific characteristics defined in the appended claims.
Substantially, the invention is based on the concept of providing an anti-balloon device in which the continuous lateral surface of the frustum-shaped shield-like element is replaced by a bottomless basket-like structure comprising a set of cylindrical rods which are arranged, according to one of the embodiments, along the generatrices of an ideal frustum-shaped solid, are mutually angularly equidistant, and are connected by end elements and, in particular, removably connected to a pair of axially spaced end rings which have appropriate diameters and define the ideal frustum-shaped solid.
According to another embodiment of the invention, the ideal solid can be cylindrical or oval and cut in half along its maximum diameter.
According to still another embodiment, the basket can be provided starting from a single continuous rod or bar which is bent into a coil with straight formations running longitudinally, preferably substantially along the generatrices of the ideal geometric solid formed by the bottomless basket and with end formations, with respect to the basket, which are bent in a U-shape and are joined to the contiguous straight formations and are an integral part thereof.
According to still another embodiment of the invention, the cylindrical removable rods interposed between the end rings are straight, variable in number and chosen according to the friction that the device is allowed to apply to the type of thread being unwound without said thread being subjected to damage and breaks.
The invention might also be used in the front unwinding of the textile thread from a cross-wound spool.